The use of optical and/or optoelectronic devices is increasing in communications applications. These devices can include light sensors that receive light signals from a waveguide. These light sensors use a light-absorbing medium that absorbs light received at the light sensor. The bandwidth of the light sensor is the range of wavelengths that can effectively be detected by the light sensor. The bandwidth of the light sensor is generally determined by the material used for the light-absorbing medium. For instance, many light sensors use germanium for the light-absorbing medium.
Light used for communications applications typically has a wavelength in the range of 1500-1600 nm. However, when the wavelength becomes longer than 1550 nm, the absorption of light by germanium decreases because the photon energy falls below the germanium bandgap. As a result, the light sensors that use germanium for detection of wavelengths longer than 1550 nm are typically long and/or use thick layers of germanium in order to increase the opportunity for the germanium to absorb the light. However, increasing the length and/or thickness of the germanium increases the capacitance of the light sensor and accordingly ends up reducing the bandwidth of the light sensor. As a result, there is a need for a light sensor construction that improves bandwidth without increasing capacitance.